Indeed if you actually are using Haskell in production, there's no way your coworkers won't be able to understand a simple signature with three classes. They probably aren't Haskell beginners. Please, have some confidence in your coworkers' intelligence and reasoning ability.

The issue isn't understanding the signature per se. The point is that type signatures aren't always enough to figure out what a function does.

That’s a good point, but often a type signature constrains the possible programs to such a degree that there is only one nonsensical program that can be written with that signature.

That's rarely the case for effectful code, which is where you'd typically see multiple monadic type class constraints.